Electro-anatomic mapping is now widely used to guide treatment of heart rhythm disturbances. This involves the following steps i) 3D heart surface geometry is reconstructed for the chamber (or chambers) of concern ii) electrical signals (time varying electric potentials) are recorded at a number of registered points on the heart surface, and iii) electrical activity throughout the region is rendered, in time and space. Based on this information, likely sources of rhythm disturbance in the heart wall are then located and ablated.
Atrial fibrillation (AF) is the most common heart rhythm disturbance and its prevalence increases with age and heart disease. AF impairs exercise performance, may cause discomfort and increases the risk of stroke. The long-term success of treating persistent and permanent AF with conventional electro-anatomic mapping and ablation methods has been disappointing, see Brooks A G, Stiles M K, et al. Heart Rhythm. 2010; 7:835-846.
For example, the widely used CARTO (Biosense Webster, Inc.) mapping system sequentially records electrical activity and 3D coordinates at individual points across the endocardial surface of a heart chamber. This enables reliable electro-anatomic maps to be reconstructed when electrical activity is repetitive, but not in persistent or permanent AF when spatio-temporal electrical activity is highly variable.
This has driven recent development of methods for near real-time mapping and analysis of electrical activity in persistent and permanent AF using intracardiac catheters that record electrical activity simultaneously at multiple 3D locations. In this setting, real-time covers acquisition, analysis and visualization processes that are completed within a few seconds at most.
One approach here is to use flexible multi-electrode basket catheters that make direct contact with the atrial surface. Electrical activity can be mapped throughout the cardiac cycle provided that electrodes remain in contact with the chamber wall and their 3D position is known.
The Constellation catheter (Boston Scientific, Inc.) is an expandable basket catheter with 64 electrodes to record potentials. Constellation catheters in a contact mapping system have detected rotors (or focal drivers) in patients with AF for the first time and almost doubled the success rate of catheter ablations by targeting rotor circuits directly [Narayan S M, Krummen D E, et al. JACC. 2012; 60:628-636-846]. This has led to the development of improved catheter design and novel phase mapping software by Topera Medical, Inc.
However, such contact mapping approaches have a number of inherent limitations. For successful real-time mapping across a complete atrial chamber, catheter dimensions need to be matched to those of the chamber of interest. Even if this can be done, the complexity of atrial anatomy means that some regions cannot be mapped adequately. Basket catheters with dimensions appropriate for global atrial mapping cannot easily be introduced into the atrial appendages or into the junctions of the pulmonary veins. Furthermore, a significant number of electrodes will not make good contact with the chamber wall throughout the cardiac cycle, which further limits anatomic resolution. Finally, the presence of a large basket catheter in an atrial chamber constrains deployment and positioning of other devices such as ablation catheters.
An alternate approach is to use noncontact mapping methods. Here, electrical activity is measured on a surface adjacent to the inner or outer surface of the cardiac chamber of interest and is then mapped onto the heart surface in question using inverse problem techniques. St. Jude Medical, Inc. markets a catheter and mapping system intended for noncontact 3D electro-anatomic mapping. The catheter consists of a 64-electrode array mounted on an inflatable balloon, but this device is not widely used for mapping AF. Reasons for this are that the closed balloon partially occludes the atrial chamber. Also, the electrodes on the balloon are often too far from the atrial wall for accurate reconstruction of surface activation (atrial dilatation is common in longstanding persistent AF).
Acutus Medical, Inc. is developing a complete mapping system based on an expandable basket catheter that contains 42 electrodes as well as ultrasound probes. With this approach, electrical activity recorded with a multi-electrode basket catheter in an atrial cavity is used to estimate an equivalent electrical dipole distribution within the atrial wall. A weakness of this approach is that the distribution is an inferred measure that cannot be equated directly with the surface potentials measured by clinicians during the ablation process. Furthermore, the low channel count constrains the spatial resolution that can be achieved and the dimensions of the catheter preclude its use in the atrial appendages or pulmonary vein junctions.
Cardiolnsight Technologies, Inc. maps electrical activity measured on the body surface with a multi-electrode vest onto the epicardial surface of the heart using an inverse method. The approach is non-invasive, but it requires accurate 3D anatomic representations of body surface and epicardial geometry using computed tomography (CT) or magnetic resonance imaging (MRI). Weaknesses include the lack of spatial resolution in mapping atrial electrical activity and the fact that the epicardial electrical activity reconstructed with this approach cannot be directly related to the endocardial activity recorded by clinicians during AF ablation.